Overview
Knee arthritis is the wearing away of the cartilage that caps the femur, tibia and kneecap, until bone rubs on bone. As the cushion thins, the bone beneath it thickens and grows spurs, the joint lining becomes inflamed and produces fluid, and the knee stiffens and drifts into a bow-legged or knock-kneed shape. It affects the three compartments unevenly: the medial (inner) compartment wears first in most patients, the patellofemoral compartment in a smaller group, and all three in advanced disease.
Arthritis cannot be reversed, so treatment is about managing the joint for as long as possible and replacing it when management no longer works. Where a patient sits on that path is decided by how much cartilage is left on weight-bearing X-rays, how many compartments are involved, and how much the knee limits their walking distance, sleep, stairs and work. X-ray severity and symptoms often do not match, and Dr. O'Donnell treats the symptoms.
Common Symptoms
- Aching pain with walking and stairs that in later stages persists at rest and wakes you at night
- Stiffness for the first minutes after sitting or on getting out of bed, easing with movement
- Swelling after activity and a grinding or crunching sensation with bending
- Loss of full straightening, and a knee that looks more bowed or knock-kneed than it used to
- Shrinking walking distance and avoidance of stairs, kneeling and low chairs
Not every painful knee over 50 is arthritis. Sudden joint-line pain with catching after a twist suggests a degenerative meniscus tear; pain confined to the front of the knee with stairs and sitting suggests patellofemoral pain; a single well-defined sore spot in a younger patient is more likely a focal cartilage injury.
Causes & Risk Factors
Cartilage wears with age, but not evenly. Prior injury is the largest modifiable factor: an ACL tear, a meniscus tear treated by removing tissue, or a fracture into the joint each raise the lifetime risk in that knee several-fold, which is why a former college soccer player or a skier with an old tibial plateau fracture can have arthritis at 45. Alignment concentrates load on one compartment; body weight multiplies the force across the knee with every step; heavy lifting, squatting and kneeling at work accelerate wear. Inflammatory arthritis (rheumatoid, psoriatic, gout) is a separate process managed with a rheumatologist. Under 50, arthritis usually has a specific cause; over 60 it is most often the wear of decades.
How It Is Diagnosed
The exam records what the X-ray cannot: how far the knee straightens and bends, whether an effusion is present, crepitus with motion, joint-line tenderness, standing alignment and gait. Dr. O'Donnell also examines the hip, because hip arthritis refers pain to the knee, and the ligaments, since a knee with an incompetent ACL is treated differently when replacement is planned.
Weight-bearing X-rays make the diagnosis. Standing front and side views plus a 45° flexed view show joint-space narrowing where it matters, and a sunrise view shows the patellofemoral compartment. Long-leg films measure alignment when partial replacement or osteotomy is being considered. MRI is rarely needed: it shows a degenerative meniscus tear in nearly every arthritic knee, which does not change the plan, and is ordered only when a mechanical symptom suggests a displaced fragment or when X-rays look too normal to explain the pain. Existing imaging can be uploaded through mymedicalimages.com ahead of a first visit.
Treatment Options
Non-operative care
Most patients are managed without surgery for years. Load management: shifting from running to cycling, swimming or elliptical, and losing weight where it applies, since each pound lost takes roughly four pounds off the knee with every step. Strengthening: a quadriceps and hip program with a physical therapist, which reduces pain as reliably as any medication. Bracing: an unloader brace that shifts weight off a single worn compartment. Injections: an ultrasound-guided corticosteroid injection reduces pain and swelling in a flared knee for weeks to a few months and is limited to a few a year; hyaluronic acid is an option for mild to moderate disease. Arthroscopy has almost no role in arthritis and is reserved for a knee that is truly locking on a displaced fragment.
Partial or total knee replacement
When the X-ray shows bone on bone and the knee limits walking, work or sleep despite the measures above, replacement is the reliable treatment. In a patient whose wear is confined to the medial compartment, with an intact ACL, good motion and a correctable deformity, a partial (unicompartmental) replacement resurfaces only that side, preserves the rest of the native knee, and recovers faster with a more natural feel. For disease in two or three compartments, significant deformity or a stiff knee, Dr. O'Donnell performs a total knee replacement, resurfacing the femur, tibia and usually the kneecap with metal and polyethylene components. Age alone neither rules out replacement nor indicates it.
Recovery & What to Expect
Rehabilitation starts the day of surgery, with full weight bearing on a walker or crutches. The most important task of the first six weeks is regaining motion, because a stiff knee is the most common problem after replacement and is far easier to prevent than to fix. Dr. O'Donnell's protocol runs as follows.
| Phase | Timing | What happens |
|---|---|---|
| Motion & mobility | Weeks 0–2 | Weight bearing as tolerated with a walker or crutches. Quad sets, straight-leg raises, heel slides, full passive extension with heel props, gait and transfer training. Goals: full extension and flexion of at least 90°. |
| Progressive motion & strength | Weeks 2–6 | Flexion progressed toward 120°; walker weaned to a cane and then nothing. Mini-squats, step-ups, stationary bike, balance and stair training. Advance at 115° of flexion and a normal gait without an aid. |
| Strengthening | Weeks 6–12 | Progressive resistance, single-leg balance, endurance conditioning and functional stair work until independent with daily activities. |
| Return to activity | Months 3–6 | Walking, cycling, swimming and golf as cleared. Long-term activity is low impact — no running or jumping. |
Desk work is usually possible at 2 to 4 weeks; driving once off narcotic medication and able to brake firmly, typically 4 to 6 weeks for a right knee; golf, cycling and swimming from about 3 months. Partial replacement follows the same sequence and tends to move faster. The protocol is available as a PDF: total knee replacement.
Frequently Asked Questions
Can knee arthritis be reversed or can cartilage grow back?
No. Worn cartilage does not regrow, and no injection or supplement rebuilds it. What can change is how the knee feels: losing weight, strengthening the quadriceps and hip, shifting to low-impact exercise and using injections well can keep a moderately arthritic knee comfortable for years. Replacement is reserved for when those measures stop working.
Do injections work for knee arthritis?
A corticosteroid injection reliably reduces pain and swelling in a flared knee for several weeks to a few months and is limited to a few per year. Hyaluronic acid helps a subset of patients with mild to moderate wear and can be repeated. Dr. O'Donnell places both under ultrasound guidance. Neither slows the arthritis; both give temporary relief.
When is it time for a knee replacement?
When the X-ray shows bone on bone and the knee is limiting what you need to do — walking distance, stairs, work, sleep — despite therapy, bracing and injections. Patients who wait until they are severely limited recover more slowly, so the conversation happens when quality of life is suffering, not when the X-ray looks bad enough.
How long does knee replacement recovery take?
Walking with a walker the day of surgery; a cane by 2 to 3 weeks and no aid by 6; desk work at 2 to 4 weeks; driving at roughly 4 to 6 weeks. Most patients are comfortable with daily life by 3 months and keep improving for a year. Regaining full straightening and at least 115° of bend in the first six weeks is the key to the result.
Can I play golf, ski or play tennis after a knee replacement?
Walking, cycling, swimming, golf and hiking are expected. Doubles tennis and skiing on groomed runs are reasonable for patients who did them before surgery and regain good strength; running and jumping are discouraged because impact wears the polyethylene bearing. Dr. O'Donnell discusses specific sports individually once strength and motion have recovered.
This page is for general education and is not a substitute for a medical evaluation. Treatment recommendations depend on your individual diagnosis and goals. Kevin O'Donnell, MD sees patients from Coral Gables, Miami, Brickell, Pinecrest and Coconut Grove at 475 Biltmore Way, and out-of-town patients by telemedicine.